import java.util.Scanner;
public class ShapeAreaCalculator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println(" 请输⼊形状名称（正⽅形、圆形 或 三⻆形）： ");
                String shape = scanner.nextLine().trim().toLowerCase();
        if (" 正⽅形 ".equals(shape)) {
        System.out.println(" 请输⼊正⽅形的边⻓： ");
        double side = scanner.nextDouble();
        double area = calculateSquareArea(side);
        System.out.println(" 正⽅形的⾯积是： " + area);
    } else if (" 圆形 ".equals(shape)) {
            System.out.println(" 请输⼊圆形的半径： ");
            double radius = scanner.nextDouble();
            double area = calculateCircleArea(radius);
            System.out.println(" 圆形的⾯积是： " + area);
        }else if (" 三⻆形 ".equals(shape)) {
            System.out.println(" 请输⼊三⻆形的三条边⻓： ");
            double a = scanner.nextDouble();
            double b = scanner.nextDouble();
            double c = scanner.nextDouble();
            double area = calculateTriangleArea(a, b, c);
            System.out.println(" 三⻆形的⾯积是： " + area);
        } else {
            System.out.println(" 不⽀持的形状类型。 ");
        } scanner.close();
}
public static double calculateSquareArea(double sideLength) {
    return sideLength * sideLength;
}
public static double calculateCircleArea(double radius) {
    return Math.PI * radius * radius;
}
public static double calculateTriangleArea(double a, double b,
                                           double c) {
    double s = (a + b + c) / 2;
    return Math.sqrt(s * (s - a) * (s - b) * (s - c));
}
                                       }
